When we were in the army in South Africa in the early '80 it was something we do to keep ourselves busy when not on patrols. We would take an empty beer bottle and tie a string dipped in diesel around the level were you want it cut. Then you light the string and let it burn till it fall off. Then you submerge the bottle up to the heated line and the top will just pop off. A piece of sandpaper and a little sanding around the top and you have a cool glass or by adding a wooden handle a nice beer mug
